JP2010152190A - Developing device and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which can stably detect developing current without being influenced by a toner thin layer formed on a toner carrier, and to provide an image forming apparatus including the same. <P>SOLUTION: A first bias circuit 30 which applies Vslv (DC) and Vslv (AC) is connected to a developing roller 23, and a second bias circuit 31 which applies Vmag (DC) and Vmag (AC) is connected to a magnetic roller 22. A variable voltage device 33 is connected to the first and second bias circuits 30 and 31, and a current detection device 35 is connected between the developing roller 23 and the first bias circuit 30. When detecting current by the current detection device 35, Vmag (DC) is applied to be equal or in a direction in which toner moves from the developing roller 23 side to the magnetic roller 22 side relative to Vslv (DC). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus including the developing device, and in particular, uses a two-component developer composed of a magnetic carrier and a toner, The present invention relates to a drive control method for a developing device that develops an electrostatic latent image on an image carrier while holding only a charged toner on the body.

  Conventionally, as a development method using dry toner in an image forming apparatus using an electrophotographic process, a one-component development method using no carrier and a two-component developer charging a nonmagnetic toner using a magnetic carrier are used. In addition, a two-component development system is known in which an electrostatic latent image on an image carrier (photoconductor) is developed by a magnetic brush composed of toner and a carrier formed on a developing roller.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the image carrier is not disturbed by the magnetic brush. On the other hand, the toner is charged by the charge roller, and the elastic regulating blade is used on the development roller. In order to regulate the layer thickness, the toner additive adheres to the charge roller, the charging ability is lowered, and it is difficult to stably maintain the charge amount of the toner. In addition, toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects.

  Further, in the case of color printing in which color superposition is performed, since the toner is required to be transparent, it needs to be a non-magnetic toner. Therefore, full-color image forming apparatuses often employ a two-component development system that charges and conveys only toner that does not contain a carrier component. However, the two-component development method can maintain a stable charge amount for a long time and is suitable for extending the life of the toner, but is disadvantageous in terms of image quality due to the influence of the magnetic brush described above.

  As one means for solving these problems, a magnetic roller (toner supply member) is used to transfer the developer onto a developing roller (toner carrier) installed in a non-contact manner with respect to the photoreceptor (image carrier). In this case, only a non-magnetic toner is transferred onto the developing roller while leaving the magnetic carrier on the magnetic roller to form a thin toner layer, and an electrostatic latent image on the photosensitive member (image carrier) is formed by an AC electric field. A developing method for adhering toner has been proposed.

  In this developing system, noise and image density unevenness due to current leakage between the developing roller and the photosensitive member have been problems. This is because if the AC component of the developing bias applied to the developing roller in the developing region is too high, the potential difference between the surface potential of the photoconductor and the peak value of the AC voltage increases, causing a leak between the photoconductor and the developing roller. If the AC component is too low, the potential difference between the surface potential of the photoconductor and the peak value of the AC voltage becomes small, and the toner does not fly sufficiently from the developing roller onto the photoconductor, resulting in uneven image density. This is because it occurs.

  For this reason, it is necessary to select an AC voltage for the developing bias so that the above-mentioned problems do not occur. In practice, however, the forming accuracy and mounting accuracy of the developing roller and the gap (developing gap) between the photosensitive member and the developing roller are determined. The development gap and the resistance value of the developing roller differ for each development due to wear of the spacers and the like. In addition, since the ease of occurrence of a leak varies depending on the use environment of the apparatus, when the same AC voltage is selected uniformly, a leak may occur or image density unevenness may occur.

  Therefore, Patent Document 1 discloses an impedance measuring unit that measures the impedance of a developing region between an image carrier (photosensitive member) and a toner carrier (developing roller), and a current (developing current) that flows in the developing region. And a leak detection means for detecting the occurrence of a leak, and a developing device capable of selecting an optimal AC voltage that does not cause a leak or uneven image density based on the leak occurrence voltage when the leak is intentionally disclosed is disclosed Has been.

The method of Patent Document 1 utilizes the property that when the development gap between the image carrier and the toner carrier is wide, the impedance is large (development current is small), and when the development gap is narrow, the impedance is small (development current is large). This is a technique for determining the developing bias efficiently and accurately by predicting the leakage occurrence voltage from the impedance.
Japanese Patent Laid-Open No. 2005-78015

  However, if the developing current is detected in a state where the toner thin layer is formed on the toner carrier, the measurement value is likely to vary due to a change in the thickness of the toner thin layer, a change in the toner charge amount, etc., and the impedance measurement accuracy deteriorates. For this reason, it is necessary to determine the AC voltage in consideration of variations in measured values, and there has been a demand for the development of an impedance detection method that is not easily affected by the toner thin layer.

  In view of the above problems, the present invention provides a developing device capable of stably detecting a developing current without being affected by a toner thin layer formed on a toner carrier, and an image forming apparatus including the developing device. With the goal.

  In order to achieve the above object, the present invention provides a toner carrier that is disposed so as to face the image carrier in a non-contact manner, a toner supply member that forms a toner thin layer on the toner carrier using a magnetic brush, When applying a DC voltage or a DC voltage and an AC voltage to the toner supply member, applying a DC voltage and an AC voltage to the toner carrier, and applying an AC voltage to the toner carrier by the voltage application unit And a current detection unit that detects a current flowing between the image carrier and the toner carrier, wherein the voltage application unit detects the current by the current detection unit. The DC voltage applied to the toner carrier is equal to the DC voltage applied to the toner carrier, or is applied in the direction in which the toner moves from the toner carrier to the toner supply member. It is characterized by a door.

  According to the present invention, in the developing device configured as described above, the developing device includes a storage unit that stores a detection result by the current detection unit, and the current value detected by the current detection unit is stored in the storage unit at the previous detection time. An AC voltage applied between the image carrier and the toner carrier is set according to a fluctuation range from the current value.

  The present invention also provides an image forming apparatus equipped with the developing device having the above-described configuration.

  According to the first configuration of the present invention, it is possible to detect the developing current flowing between the image carrier and the toner carrier in a state where there is almost no toner thin layer on the toner carrier. Since the developing current can be detected stably without receiving, the measurement accuracy of the impedance measured based on the developing current is increased. Accordingly, the prediction accuracy of the leak generation voltage predicted from the impedance is also improved, and the AC voltage applied between the image carrier and the toner carrier can be appropriately set. In addition, since the formation of the toner thin layer on the toner carrier can be suppressed as much as possible, wasteful toner consumption can be suppressed.

  According to the second configuration of the present invention, the developing device having the first configuration includes a storage unit that stores a detection result by the current detection unit, and stores a current value detected by the current detection unit. By setting the AC voltage applied between the image carrier and the toner carrier according to the fluctuation range from the current value at the time of the previous detection stored in, the environmental changes such as atmospheric pressure and temperature / humidity from the fluctuation of the development current Therefore, the AC voltage applied between the image carrier and the toner carrier can be corrected appropriately according to changes in environmental conditions.

  Further, according to the third configuration of the present invention, by mounting the developing device having the first or second configuration, the impedance is measured based on the accurately detected developing current, and the leakage generation voltage is further reduced. It is possible to predict and set an optimal AC voltage that does not cause leakage or uneven image density, so that the image forming apparatus can simultaneously solve the occurrence of noise due to current leakage and the occurrence of uneven image density.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to the present invention. Here, a tandem color image forming apparatus is shown. In the main body of the color image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is rotated clockwise in FIG. 1 by a driving means (not shown) and sequentially transferred onto the intermediate transfer belt 8 moving adjacent to each image forming unit, and then the secondary transfer roller 9. In this case, the toner image is transferred onto the transfer paper P at once, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via a paper feed roller 12a and a registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure unit 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

  When the image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing devices 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically attached, whereby a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 4 is formed. It is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the intermediate transfer rollers 6a to 6d. Transcribed above. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and a full color image is transferred. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed only on one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 7 is distributed to the paper transport path 18 by the branching unit 14, and the secondary transfer roller 9 with the image surface reversed. Re-conveyed. Then, after the next image formed on the intermediate transfer belt 5 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed, and conveyed to the fixing unit 7 and the toner image is fixed. , And discharged to the discharge tray 17.

  FIG. 2 is a side sectional view showing a configuration of a developing device used in the image forming apparatus of the present invention. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter simply referred to as a developer) is accommodated, and the developing container 20 is divided into a first wall and a second wall by a partition wall 20a. The first and second agitating chambers 20b and 20c are divided into agitating chambers 20b and 20c, and a toner (positively charged toner) supplied from a toner container (not shown) is mixed with a carrier and agitated and charged. The stirring screw 21a and the second stirring screw 21b are rotatably arranged.

  Then, the developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and the first and second are passed through developer passages (not shown) formed in the partition wall 20a. It circulates between the stirring chambers 20b and 20c. In the illustrated example, the developing container 20 extends obliquely upward to the left, a magnetic roller 22 is disposed in the developing container 20 above the second stirring screw 21b, and the developing roller 20 is disposed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1 on the opening side (left side in FIG. 2) of the developing container 20, and the magnetic roller 22 and the developing roller 23 rotate clockwise in the drawing.

  Note that a toner concentration sensor (not shown) is disposed in the developing container 20 so as to face the first stirring screw 21a, and the toner supply port 20d is supplied from the supply device according to the toner concentration detected by the toner concentration sensor. The toner is supplied into the developing container 20 via

  The magnetic roller 22 includes a nonmagnetic rotating sleeve 22a and a fixed magnet roller body 22b having a plurality of magnetic poles (here, five poles) contained in the rotating sleeve. The developing roller 23 is composed of a non-magnetic developing sleeve, and the magnetic roller 22 and the developing roller 23 are opposed to each other at a facing position (opposing position) with a predetermined gap.

  Further, a spike cutting blade 25 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 22 (front and back direction in FIG. 2), and the spike cutting blade 25 rotates in the rotational direction of the magnetic roller 22 (clockwise in the figure). Around the opposite position between the developing roller 23 and the magnetic roller 22. A slight gap (gap) is formed between the front end of the spike cutting blade 25 and the surface of the magnetic roller 22.

  The developing roller 23 is connected to a first bias circuit 30 that applies a DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)). A second bias circuit 31 for applying a voltage (hereinafter referred to as Vmag (DC)) and an alternating voltage (hereinafter referred to as Vmag (AC)) is connected. The first bias circuit 30 and the second bias circuit 31 are grounded to a common ground.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Then, a magnetic brush (not shown) is formed on the magnetic roller 22. After the layer thickness of the magnetic brush on the magnetic roller 22 is regulated by the ear cutting blade 25, the magnetic brush 22 is conveyed to the opposite portion between the magnetic roller 22 and the developing roller 23, and Vmag (DC) applied to the magnetic roller 22 and the developing roller 23. A toner thin layer is formed on the developing roller 23 by a potential difference ΔV with respect to Vslv (DC) applied to the toner and a magnetic field.

  The thickness of the toner layer on the developing roller 23 varies depending on the resistance of the developer and the rotational speed difference between the magnetic roller 22 and the developing roller 23, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 23 is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  FIG. 3 is a diagram illustrating an example of a bias waveform applied to the developing roller 23 and the magnetic roller 22. As shown in FIG. 3A, the developing roller 23 has a combined waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 superimposed on Vslv (DC) is a first bias circuit. 30 applied. Further, the magnetic roller 22 has a second combined waveform Vmag (broken line) in which Vmag (DC) has a peak-to-peak value of Vpp2 and a rectangular wave Vmag (AC) having a phase different from Vslv (AC). Applied from the bias circuit 31.

  Accordingly, the voltage applied between the magnetic roller 22 and the developing roller 23 (hereinafter referred to as MS) is a composite waveform Vmag-Vslv having Vpp (max) and Vpp (min) as shown in FIG. Become. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 23 by the magnetic brush is conveyed to a facing portion between the photosensitive drum 1 a and the developing roller 23 by the rotation of the developing roller 23. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 23, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  The remaining toner that is not used for development is conveyed again to the opposite portion between the developing roller 23 and the magnetic roller 22 and collected by the magnetic brush on the magnetic roller 22. Then, the magnetic brush is peeled off from the magnetic roller 22 at the same polarity portion of the fixed magnet roller body 22b, and then formed again on the magnetic roller 22 as a two-component developer uniformly charged with an appropriate toner concentration. And conveyed to the ear cutting blade 25.

  Further, a voltage variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31, and Vslv (DC), Vslv (AC) applied to the developing roller 23 and Vmag applied to the magnetic roller 22. (DC) and Vmag (AC) can be varied. Further, a current detector 35 is connected between the developing roller 23 and the first bias circuit 30. The current detection device 35 detects the developing current that flows when Vslv (AC) is applied from the first bias circuit 30 to the developing roller 23, so that it is between the photosensitive drum 1 a and the developing roller 23 (hereinafter referred to as between DS). ) Impedance can be measured.

  The control unit 37 transmits a control signal to the voltage variable device 33 and is applied from the first bias circuit 30 and the second bias circuit 31 to Vslv (DC), Vslv (AC), Vmag (DC), and Vmag (AC). To control. Further, the impedance between the DSs is measured based on the development current detected by the current detection device 35, and the gap between the DSs (development gap) is predicted from the measured impedance. Since the narrower the development gap, the easier it is for leaks to occur. Therefore, the peak-to-peak value of the AC voltage applied between the DSs (hereinafter referred to as Vpp between DSs) can be estimated by predicting the gap between DSs. Can be set.

  The storage unit 39 includes, for example, a readable / writable RAM (Random Access Memory). In addition to the control program used by the control unit 37, the development current detected by the current detection device 35, the impedance measured based on the development current, and the like. Data necessary for control, such as the set Vpp between DS and the peak-to-peak value of the AC voltage applied between the magnetic roller and the developing roller (hereinafter referred to as Vpp between MS), is stored. Note that the control unit 37 and the storage unit 39 may be combined with the control unit and the storage unit of the entire image forming apparatus 100, or may be arranged independently to control the developing devices 3a to 3d.

  In the present invention, when current is detected by the current detection device 35, Vmag (DC) applied to the magnetic roller 22 is equal to Vslv (DC) applied to the developing roller 23, or toner is used as the developing roller. It is applied in the direction of moving from the 23 side to the magnetic roller 22 side. For example, when using a positively charged toner whose charging direction is positive (plus side), Vslv (DC) ≧ Vmag (DC), and when using a negatively charged toner whose charging direction is negative (minus side), Vslv (DC) ≦ Vmag (DC).

  As a result, the current can be detected with almost no toner thin layer on the developing roller 23, and the developing current can be stably detected without being affected by the toner thin layer. Variation in impedance measured based on the result is suppressed, and the measurement accuracy is increased. Accordingly, the setting accuracy of the inter-DS Vpp is also improved.

  Furthermore, factors that cause variations in the measured impedance value include variations in the gap between DS, changes in the thickness of the toner layer, changes in charge amount, and changes in environmental conditions such as atmospheric pressure and temperature / humidity. Since the development current can be detected under conditions with little influence and the gap between the DSs does not change from the time of manufacturing the apparatus, the change in the development current is considered to be a change in environmental conditions. Therefore, the development current is stored in the storage unit 39, and compared with the development current measured after a certain time, the inter-DS Vpp can be appropriately corrected according to changes in atmospheric pressure, temperature and humidity, and the like.

  Specifically, an environmental correction table that defines correction values of development conditions (Vslv (DC), Vslv (AC), etc.) with respect to the fluctuation amount of the environmental conditions is stored in the storage unit 39 and corrected according to the fluctuation range. I do. For example, the lower the atmospheric pressure, the lower the development current and the easier it is to leak. In addition, the higher the temperature and the lower the humidity, the lower the development current and the more likely leakage occurs.

  That is, if the development current measured after a certain time has elapsed, it means any one of pressure drop, temperature rise, and humidity drop. In that case, the Vpp between DS is reduced so that no leak occurs. Just do it. Conversely, if the development current measured after a certain time has elapsed, the Vpp between DS may be increased. Furthermore, if the temperature and humidity inside or outside the apparatus are separately detected using a temperature and humidity sensor, correction based on changes in temperature and humidity can be performed separately, so that the accuracy of correction can be further improved.

  FIG. 4 is a flowchart showing a procedure for setting the Vpp between DSs in the image forming apparatus provided with the developing device of the present invention. First, in response to a control signal from the control unit 37, the voltage variable device 33 applies a predetermined Vslv (AC) from the first bias circuit 30 to the developing roller 23, and the current detecting device 35 detects the developing current (step S1). . The detected current value is stored in the storage unit 39. Then, the elapsed time after the current detection is measured (step S2), and when the predetermined time has elapsed (YES in step S3), Vslv (AC) is applied again to re-detect the development current (step S4).

  Next, the development current fluctuation range is calculated by comparing the re-detected development current with the development current at the previous detection stored in the storage unit 39 (step S5). Then, it is determined whether or not the development current has fluctuated by a predetermined width or more (step S6). If there is a fluctuation of a predetermined width or more, it is then determined whether or not the development current has decreased (step S7). If the development current has decreased, the Vpp between DS is reduced according to the amount of decrease in the development current. Correction is performed (step S8). On the other hand, when the development current becomes high, correction is performed to increase the Vpp between DSs according to the increase amount of the development current (step S9).

  If the fluctuation range of the development current is smaller than the predetermined width in step S6, the DS Vpp is maintained. Thereafter, when the Vpp between DSs is corrected (steps S8 and S9), the development current redetected in step S4 is overwritten in the storage unit 39 as the development current at the previous detection, and the process returns to step S2, and thereafter the same control is performed. Is repeated (steps S3 to S8).

  In the control example of FIG. 4, when the image forming apparatus is installed under the user, a change in environmental conditions at the installation location can be detected by a change in development current. It is possible to set the optimum Vpp between DSs that does not cause image defects due to.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in each of the above-described embodiments, the reversal development method in which the toner is ejected to the exposed portion on the surface of the photoreceptor has been described as an example. It is applicable to.

  Further, the present invention is not limited to the tandem type color printer shown in FIG. 1, and includes a developing device such as a digital or analog type monochrome copying machine, a monochrome printer, a rotary developing type color printer, a color copying machine, a facsimile, or the like. The present invention can be applied to various image forming apparatuses. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

  Using the test machine as shown in FIG. 1 in which the developing device of the present invention shown in FIG. 2 is mounted, leakage is generated and detected by changing Vslv (DC) and Vmag (DC). The variation and toner adhesion to the image area were compared. The test was performed in a cyan image forming portion Pa including the photosensitive drum 1a and the developing device 3a.

The test machine conditions were a printing speed of 40 sheets / minute, a photosensitive drum peripheral speed of 200 mm / sec, and a drum surface potential of 300 V for the white background potential (V0) and 20 V for the image portion potential (VL). Also, the developing roller is alumite-treated, the developing roller has a peripheral speed ratio of 1.3 with respect to the photoreceptor (forward rotation on the opposite surface), and the magnetic roller has a peripheral speed ratio with respect to the developing roller. 1.5 (counter rotation on the facing surface). In addition, the DS gap was 120 μm, and the MS gap was 300 μm. As the developer, a two-component developer comprising a positively charged toner having an average particle diameter of 6.8 μm, a volume resistivity of 10 ¹⁰ Ω, a saturation magnetization of 65 emu / g, and a coated ferrite carrier having an average particle diameter of 45 μm is used. The mixing ratio (T / C) was 12% by weight.

  The voltage application conditions to the developing roller were Vslv (DC) = 50 V, Vslv (AC) = 900 V, frequency 4.5 kHz, Duty = 45%. The voltage application conditions between the MSs were Vmag (DC) −Vslv (DC) = 200V, Vmag (AC) −Vslv (AC) = 1800V, frequency = 4.5 kHz, Duty = 75%.

  As an evaluation method, when Vslv (DC) applied to the developing roller and Vmag (DC) applied to the magnetic roller are both 75 V (Invention 1), Vslv (DC) is 75 V, and Vmag (DC) is 0 V. In this case (Invention 2), when Vslv (DC) was 75 V and Vmag (DC) was 275 V (Comparative Example 1), the development current was detected 10 times each, and the average current value and its deviation were obtained. . The evaluation results are shown in Table 1.

  As is clear from Table 1, in Comparative Example 1 in which leakage occurred under normal development conditions in which Vslv (DC) was 75 V and Vmag (DC) was 275 V, the average value of the development current was 4.352 mA. The deviation of the measured value was 0.0622. On the other hand, in the present invention 1 in which Vslv (DC) and Vmag (DC) are both 75 V, and in the present invention 2 in which Vmag (DC) is 0 V, the average value of the developing current is 4.3442 mA, 4.4292 mA. Although it was almost equivalent, the deviation of the measured values was 0.0488 and 0.0461, which were smaller than the comparative example.

  The reason for this is that in Comparative Example 1, a voltage is applied in the direction in which the toner moves from the magnetic roller to the developing roller, and a toner layer is formed on the developing roller, so that the developing current tends to vary. 1, the potential difference ΔV between the MSs is 0V, so that the toner movement from the magnetic roller to the developing roller is suppressed, and the development current variation is suppressed. In the second aspect of the present invention, voltage is applied in the direction in which the toner moves from the developing roller to the magnetic roller, so that no toner moves from the magnetic roller to the developing roller. It is thought that it became small.

  From the above results, by setting Vslv (DC) and Vmag (DC) so that toner movement from the magnetic roller to the developing roller does not occur when the developing current is detected, the variation in the measured value of the developing current can be reduced. It was confirmed that impedance measurement using a developing current and prediction of leakage generation voltage can be performed with high accuracy. Here, the test was performed in the cyan image forming portion Pa, but it has been confirmed that similar results can be obtained in the magenta, yellow, and black image forming portions Pb to Pd.

  Using the same test machine as in Example 1, the change in development current when the gap between DSs was changed stepwise was compared between Vmag (AC) = 0V and Vmag (AC) = 1800V. . The conditions of the testing machine were the same as in Example 1, and the gap between DS was maintained while maintaining Vslv (DC) = 75 V, Vmag (DC) = 0 V, and Vslv (AC) = 900 V at a temperature of 32.5 ° C. and a humidity of 80%. The development current was detected in steps of 100 μm, 120 μm, 150 μm, and 200 μm. The results are shown in Table 2.

  As is apparent from Table 2, when Vmag (AC) = 0 V, the developing current decreases as the DS gap becomes wider, so it is considered that the error in predicting the DS gap from the current value is reduced. On the other hand, when Vmag (AC) = 1800V, the variation in the measured value is large, and as the gap between DSs widens, the development current decreases as a whole, but there are also areas where the development current partially increases. It is considered that the error in predicting the gap becomes large.

  Using the same testing machine as in Example 1, the occurrence of leakage when the temperature, humidity, or atmospheric pressure changed was investigated. The conditions of the testing machine are the same as in Example 1, and the Vpp between DSs at 25 ° C., 50%, 1 atm (1013 hPa) is 1300 V, and the Vpp between DSs is controlled according to the change in the development current (this The occurrence of leakage was observed in Invention 3) and in the case where control of Vpp between DSs was not performed (Comparative Example 2). The results are shown in Tables 3-5.

  As is apparent from Tables 3 to 5, in the present invention 3 in which the Vpp between DSs was reduced by 100 V when the development current was reduced by 0.02 mA, no occurrence of leakage due to changes in temperature, humidity, or atmospheric pressure was observed. . On the other hand, in Comparative Example 2 in which the Vpp between DSs was always constant (1300 V), leakage due to a temperature rise, a humidity drop, and a pressure drop was observed. From this result, it was confirmed that a change in environmental conditions was detected by measuring the development current, and the occurrence of leak could be suppressed by controlling the Vpp between DSs according to the fluctuation range of the development current.

  Each of the above-described embodiments is merely an example of the present invention, and the drum surface potential, conditions for applying voltage to the developing roller and the magnetic roller, and the like can be appropriately set according to the specifications of the apparatus and the usage environment. .

  INDUSTRIAL APPLICABILITY The present invention can be used in a developing device that develops an electrostatic latent image on an image carrier by holding only a charged toner on the toner carrier using a toner supply member. When the current flowing between the toner carrier and the toner carrier is detected, the DC voltage applied to the toner carrier is equal to the DC voltage applied to the toner carrier, or the toner moves from the toner carrier to the toner carrier. It is applied in the direction.

  As a result, the development current can be detected stably without being affected by the toner thin layer, so that the development of the impedance measurement accuracy and the prediction accuracy of the gap between the image carrier and the development roller and the voltage causing the leakage is high. An apparatus can be provided. In addition, since the formation of the toner thin layer on the toner carrier can be suppressed as much as possible, wasteful toner consumption can be suppressed.

  Further, since the development current can be detected under a condition where the influence of the toner thin layer is small, the cause of the change in the development current is a change in environmental conditions. Therefore, if an AC voltage applied between the image carrier and the toner carrier is set according to the fluctuation range from the previous detection of the current value detected by the current detection means, between the image carrier and the toner carrier. A developing device capable of appropriately correcting the applied AC voltage in accordance with changes in environmental conditions.

FIG. 1 is a schematic diagram showing an overall configuration of an image forming apparatus equipped with a developing device of the present invention. These are side surface sectional views which show the structure of the developing device of this invention. These are figures which show an example of the bias waveform applied to a developing roller and a magnetic roller. These are the flowcharts which show the setting procedure of Vpp between DS in the image forming apparatus provided with the developing device of the present invention.

Explanation of symbols

1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 21a First stirring screw 21b Second stirring screw 22 Magnetic roller (toner supply member)
23 Developing roller (toner carrier)
25 Bone cutting blade 30 First bias circuit (voltage application means)
31 Second bias circuit (voltage applying means)
33 Voltage variable device 35 Current detection device (current detection means)
37 control section 39 storage section (storage means)
100 Image forming apparatus Pa to Pd Image forming unit

Claims (3)

A toner carrier that is disposed to face the image carrier in a non-contact manner;
A toner supply member that forms a toner thin layer on the toner carrier using a magnetic brush;
Voltage application means for applying a DC voltage or a DC voltage and an AC voltage to the toner supply member, and applying a DC voltage and an AC voltage to the toner carrier;
Current detection means for detecting a current flowing between the image carrier and the toner carrier when an AC voltage is applied to the toner carrier by the voltage application means;
In a developing device having
The voltage application means is configured such that, when the current is detected by the current detection means, the DC voltage applied to the toner supply member is equal to the DC voltage applied to the toner carrier, or the toner supply from the toner carrier. A developing device, wherein the toner is applied to the member in a direction in which the toner moves.   The image bearing unit has a storage unit that stores a detection result of the current detection unit, and the image bearing unit according to a fluctuation range of a current value detected by the current detection unit from a current value at the previous detection stored in the storage unit. The developing device according to claim 1, wherein an AC voltage applied between a body and the toner carrier is set.   An image forming apparatus on which the developing device according to claim 1 is mounted.

Images